The present invention relates to a rotary compressor which may be advantageously employed in an air conditioning system of an automotive vehicle for compressing a refrigerant fluid.
Rotary compressors are well known in the art which comprise a housing formed with a bore, fluid inlets and outlets communicating with the bore and a rotor mounted in the bore in such a manner that rotation thereof causes a working fluid such as a refrigerant to be compressively displaced from the inlet to the outlet. The rotor is typically provided with radial slots and vanes which are slidable retained in the slots and urged into sealing engagement with the inner wall of the bore. The rotor is eccentrically or similarly disposed in the bore in such a manner that upon rotation of the rotor the vanes divide the bore into fluid chambers of progressively varying volume. The compressor is designed so that the fluid chambers increase in volume in the vicinity of the inlet and decrease in volume in the vicinity of the outlet so that the fluid is sucked into the fluid chambers through the inlet and discharged therefrom through the outlet at elevated pressure. Due to the sealing effect of the vanes the compressor operates on the positive displacement principle.
A unique method has recently been devised to lubricate the rotor without the provision of a separate oil pump. An oil sump is provided below the compressor housing which communicates with the fluid outlet. In this manner, the oil in the oil sump is subjected to the output pressure of the fluid. An oil passageway leads from the oil sump to the inner portion of the rotor and to the fluid inlet in such a manner that oil is forced from the pressurized oil sump to the interior of the rotor and the low pressure fluid inlet.
The rotor comprises a drive shaft and a rotor body fixed to the shaft, the vane slots being formed in the rotor body. The oil passageway leads to the radially inner portions of the vane slots between the vanes and the shaft so that the pressurized oil not only lubricates the areas of sliding contact between the vanes and the walls of the respective slots but also urges the vanes radially outwardly into sealing engagement with the inner wall of the bore.
The oil is sucked along with the working fluid into the fluid chambers in the bore and lubricates the areas of sliding contact between the outer ends of the vanes and the wall of the bore. At the fluid outlet, the oil is separated from the working fluid and returned to the oil sump.
Although a compressor having this configuration is effective and efficient in operation and enables a substantial reduction in component parts over a compressor which comprises a separate forced feed oil pump, a problem exists in the basic design in that the vanes are urged into sealing engagement with the wall of the bore with a greater force in the inlet portion of the bore than in the outlet portion thereof. This is because the working fluid or refrigerant pressure in the inlet portion is below atmospheric whereas the pressure in the outlet portion is substantially above atmospheric due to the action of the compressor. The radially outward urging force applied to the vanes must be sufficient to prevent working fluid from blowing past the vanes in the tangential direction and overcome the inward force of the working fluid in the radial direction in the outlet portion of the bore. If the same radially outward urging force is applied to the vanes in the inlet portion of the bore, which is the case in the basic design, the pressure between the vanes and the wall of the bore is greater in the inlet portion than in the outlet portion. This is because the pressure is below atmospheric in the inlet portion and the working fluid does not urge the vanes radially inwardly against the pressure of the oil in the slots as is the case in the outlet portion. The pressure between the vanes and the wall of the bore is therefore excessive in the inlet portion.
As a natural consequence of this action, the friction is excessive in the inlet portion which causes premature wear of the vanes and bore wall. In addition, the torque required to rotatably drive the rotor is excessive requiring an unnecessarily large motor and a large flywheel to overcome the large variation in torque effort.